Atherosclerosis and other peripheral vascular diseases affect the quality of life of millions of people. Therefore, considerable attention has been directed towards understanding the etiology of hypercholesterolemia and hyperlipidemia and development of effective therapeutic strategies.
Hypercholesterolemia has been defined as plasma cholesterol level that exceeds arbitrarily defined value called “normal” level. Recently, it has been accepted that “ideal” plasma levels of cholesterol are much below the “normal” level of cholesterol in the general population and the risk of coronary artery disease (CAD) increases as cholesterol level rises above the “optimum” (or “ideal”) value. There is clearly a definite cause and effect-relationship between hypercholesterolemia and CAD, particularly for individuals with multiple risk factors. Most of the cholesterol is present in the esterified forms with various lipoproteins such as Low density lipoprotein (LDL), Intermediate density lipoprotein (IDL), High density lipoprotein (HDL) and partially as Very low density lipoprotein (VLDL). Studies clearly indicate that there is an inverse correlationship between CAD and atherosclerosis with serum HDL-cholesterol concentrations (Stampfer et al., N. Engl. J. Med., 325 (1991), 373-381). The risk of CAD increases with increasing levels of LDL and VLDL.
In CAD, generally “fatty streaks” in carotid, coronary and cerebral arteries, are found which are primarily free and esterified cholesterol. Miller et al., (Br. Med. J., 282 (1981), 1741-1744) have shown that increase in HDL-particles may decrease the number of sites of stenosis in coronary arteries of human, and high level of HDL-cholesterol may protect against the progression of atherosclerosis. Picardo et al., Arteriosclerosis 6 (1986) 434-441 have shown by in vitro experiment that HDL is capable of removing cholesterol from cells. They suggest that HDL may deplete tissues of excess free cholesterol and transfer it to liver, which is known as reverse cholesterol transport, (Macikinnon et al., J. Biol. chem. 261 (1986), 2548-2552). Therefore, agents that increase HDL cholesterol would have therapeutic significance for the treatment of hypercholesterolemia and coronary heart diseases (CHD).
Obesity is a disease highly prevalent in affluent societies and in the developing world and is a major cause of morbidity and mortality. It is a state of excess body fat accumulation. The causes of obesity are unclear. It is believed to be of genetic origin or promoted by an interaction between the genotype and environment.
Irrespective of the cause, the result is fat deposition due to imbalance between the energy intake versus energy expenditure. Dieting, exercise and appetite suppression have been a part of obesity treatment. There is a need for efficient therapy to fight this disease since it may lead to coronary heart disease, diabetes, stroke, hyperlipidemia, gout, osteoarthritis, reduced fertility and many other psychological and social problems.
Diabetes and/or insulin resistance is yet another disease which severely effects the quality of large population in the world. Insulin resistance is the diminished ability of insulin to exert its biological action across a broad range of concentrations. In insulin resistance, the body secretes abnormally high amounts of insulin to compensate for this defect; failing which, the plasma glucose concentration inevitably raises and develops into diabetes. Among the developed countries, diabetes mellitus is a common problem and is associated with a variety of abnormalities including obesity, hypertension, hyperlipidemia (J. Clin. Invest., 75 (1985) 809-817; N. Engl. J. Med 317 (1987) 350-357; J. Clin. Endocrinol. Metab., 66 (1988) 580-583; J. Clin. Invest., 68 (1975) 957-969) and other renal complications (patent publication No. WO 95/21608). It is now increasingly being recognized that insulin resistance and relative hyperinsulinemia have a contributory role in obesity, hypertension, atherosclerosis and type 2 diabetes mellitus. The association of insulin resistance with obesity, hypertension and angina has been described as a syndrome having insulin resistance as the central pathogenic link-Syndrome-X.
Hyperlipidemia is the primary cause for cardiovascular (CVD) and other peripheral vascular diseases. High risk of CVD is related to the higher LDL (Low Density Lipoprotein) and VLDL (Very Low Density Lipoprotein) seen in hyperlipidemia. Patients having glucose intolerance/insulin resistance in addition to hyperlipidemia have higher risk of CVD. Numerous studies in the past have shown that lowering of plasma triglycerides and total cholesterol, in particular LDL and VLDL and increasing HDL cholesterol help in preventing cardiovascular diseases.
Peroxisome Proliferator Activated Receptors (PPARs) are orphan receptors belonging to the steroid/retinoid receptor super family of ligand activated transcription factors. (Wilson T. M. and Wahli W., Curr. Opin. Chem. Biol., 1997, Vol. 1, 235-241). Three mammalian Peroxisome Proliferator Activated Receptors (PPARs) have been isolated and termed PPAR-α, PPAR-γ and PPAR-δ. These PPARs regulate expression of target genes by binding to DNA sequence elements.
Certain compounds that activate or otherwise interact with one or more of the PPARs have been implicated in the regulation of triglyceride and cholesterol levels in animal models. (U.S. Pat. Nos. 5,847,008; 5,859,051 and PCT publications WO 97/28149; WO 99/04815.
A wealth of information exists on the influence of PPAR α agonists on the cardiovascular risk profile for example fibrate class of compounds which are weak PPAR-α agonists correct atherogenic dyslipoproteinemia. Several angiographic intervention trials have demonstrated a beneficial action of these drugs on atherosclerotic lesion progression and results from primary and secondary prevention trials show a decreased incidence of cardiovascular events. (Ricote M. and Glass C. K.; Trends in Pharmacological Sciences; 2001; 22(9); 441-443.
Despite the fact that fibrates, which are weak PPAR-α activators, reduce the plasma triglyceride levels and elevate the levels of HDL-C simultaneously, they are not the drugs of choice, because of: low efficacy requiring high doses, incidence of Myositis and contra-indicated in patients with impaired renal and hepatic function and in pregnant and nursing women.
However there has been rapid progress in the understanding of the role of PPAR-α in different pathophysiological conditions in addition to the well-documented favourable effects on lipid profile. The inflammatory activation of aortic smooth muscle cells, which is the hallmark of atherosclerosis, seems to be inhibited by the enhanced PPAR-α activity. (Vamecq J. and Latruffe N; Lancet; 1999; 354; 141-148).
Recent evidence suggests the role of PPAR-α receptors in improving insulin sensitivity. It has been demonstrated that by lowering circulatory and muscle lipids in insulin-resistant rodent models such as obese Zucker rats, high fat-fed mice and sucrose-lard fed rats, PPAR-α ligands improve insulin sensitivity and obesity. Further the lipid lowering activity of the statins has been linked to a cross talk with PPAR-α receptor in addition to limited cholesterol availability. Some clinical trials have shown improvement in insulin sensitivity indices, wherein fibrates were employed. (Guerre-Millo M, Rounalt C. and Poulain P; Diabetes; 2001; 50; 2809-2814, Muoio D. M., Way J. M. and Tanner C. J.; Diabetes; 2002; 51; 901-909, Ye J, Doyle P. J. and Iglesias M. A.; Diabetes; 2001; 50; 411-417, and Roglans N, Sanguino E. and Peris C; JPET; 2002; 302; 232-239).
Thus there is an interesting evidence for PPAR-α agonists to be used for lipid control and as per recent evidence even for insulin resistance. Limitations of the currently available medications coupled with the fact that lipid abnormalities are on the rise worldover necessitate the discovery of more potent and safer PPAR-α agonists. In continuation of our research work on PPAR agonists (U.S. Pat. Nos. 5,885,997; 6,054,453; 6,265,401: PCT application PCT/IB02/04275) to address this unmet need, a series of compounds have been synthesized which has been disclosed in the present invention.